Coalbed Methane (CBM) is a natural gas formed by geological processes in coal seams. CBM consists predominantly of methane and is considered an all-in-one natural gas resource as it serves as the source, reservoir and trap for a vast amount of potential natural gas. Typically, CBM can be found unexploited at relatively shallow depths, and because methane is stored in coal by a different means than conventional gas, more gas per unit volume can be recovered at these shallow depths. CBM may be recovered in several ways but is commonly retrieved by penetrating the borehole casing of an existing oil or gas well at a depth below the Earth's surface, and then boring a lateral channel through an adjacent coal seam using a high pressure waterjet nozzle, or blaster nozzle.
To illustrate, oil and gas wells are typically drilled by the use of rotary drilling equipment vertically into the Earth's strata. The vertically extending well holes generally include a casing usually of mild steel in the neighborhood of 4½″ to 8″ in diameter, which defines the cross-sectional area of a well for transportation of the oil and gas upwardly to the Earth's surface. However, these vertically extending wells are only useful for removing oil and gas from the general vicinity adjacent to and directly underneath the terminating downward end of the well. Thus, not all of the oil and gas in the pockets or formations in the Earth's strata, at the location of the well depth, can be removed.
Because it is time-consuming and costly to make other vertical drillings parallel and close to the first drill, a variety of means are commonly employed to extend the original well in a radial or horizontal direction. As explained, the most common means includes perforating the casing at a specific depth and then drilling a lateral channel using a high pressure waterjet nozzle. In these operations, high-pressure hoses and waterjets are often required to pass through extremely tight areas to reach the coal seam, seemingly requiring a more flexible, smaller inner-diameter hose that can reduce overall fluid pressures. A reduction in fluid pressure results in inadequate cutting power from the waterjet nozzle and, therefore, reduced drilling capacity. Therefore, it remains desirable to find improved waterjet cutting methods that may be practiced in small areas and yet still allow for substantial high-pressure fluid pumping flow rates.